>> The above code fails to type check due to instances
> overlapping. Hugs gives the following error message:
>In Hugs, there is a flag that you can set to allow overlapping instances
:s +o
In GHC, you can also set
-fallow-overlapping-instances
BTW, I use extensible union types in a "Language prototyping System" that
I am implementing and which compiles with GHC and Hugs (it is based
on Liang, Hudak and Jones paper).
You can download the source code from
"http://lsi.uniovi.es/~labra/LPS/LPS.html"
Best regards, Jose Labra
http://lsi.uniovi.es/~labra